"Generate PDF failed due to unknown reason"

Hi, @riskypotato, if I were a betting man, I'd lay odds on it. 

I do have a question for you: All applications on the Mac are defaulted to the Application folder on the hard drive. How did you get that onto an external drive?

Meanwhile, my guess is that you manually moved it over. With some applications, that might be possible, but with complex and deep applications, like anything from Adobe, they rely upon sub-applications and scripts that are supposed to be in a specific location and feeding information to other specific information. Think of it this way: you're abducted by aliens and they do not know how humans work. So, they take your hands and put them in one cage and your mouth into a different cage. They offer you food, your hands take the food, but when your hands try to put it in your mouth, it keeps on failing.

I think that message is pretty good and as confused as your hands are. 

If all of your Adobe applications are on other external drives, I suggest you uninstall them (if possible) and reinstall from scratch ONTO your main hard drive.

There still may be issues, but good luck in the meantime. Let us know how it goes.